Life on Fire

In the vast emptiness of the ocean, tectonic movements create or destroy islands.

In the Tonga archipelago, marine and land animals have chosen to live around these smoking islands that rise from the ocean depths.

The blind Alvin shrimp can find its way around the abyss.

The sooty tern soars endlessly and avoids getting wet for fear of drowning.

Not only do these animals live in a dangerous world, they depend entirely on the mood of volcanoes to survive.

Find out next how the fates of these extraordinary creatures are linked whenever an underwater eruption occurs.

(narrator) In the vast emptiness of the Pacific Ocean, a lone sooty tern is fishing.

She's a paradox.

A seabird that dares not get her wings wet for fear she will drown.

So why choose this hostile landscape, featureless save for these smoking islands?

The answer lies miles below, deep in the abyss.

The abyssal plains are home to the Alvin shrimp, another enigma.

This shrimp is blind and yet it can find its way around this inhospitable landscape.

Whenever an underwater volcano erupts, the fate of these two extraordinary creatures is linked.

Not only do they live in this dangerous world, to survive they depend entirely on the mood of the volcano.

PIONEERS OF THE DEEP (narrator) Both sooty terns and Alvin shrimps live in the Pacific Ocean, which covers a third of the earth's surface.

They're found in the most volatile region, known as the Ring of Fire.

The fire is caused by one great continental plate sliding under another, crumpling and splitting, creating the world's largest mountain ranges and deepest valleys.

And molten lava from deep in the belly of the earth explodes through the cracks, beginning its journey up towards the light.

Usually it's only when the liquid lava cools, solidifies, and the mountain it has built over millennia finally breaks the surface that the volcano makes itself known.

In Hawaii, rivers of lava are still gradually building the summit of this volcano higher and higher.

Measured from its base deep in the abyss, it is the tallest known mountain in the world.

While some volcanoes grow slowly, others explode ferociously up from the depths.

This one caught a passing sailor by surprise and in three days created three new craters.

So, sitting above the Pacific Ring of Fire, there may be several unknown, uncharted islands, waiting to be discovered.

Explorers will name them eventually, but the ocean wanderers often find them first.

For a humpback whale, on her long journey from Antarctica to the warmer waters of the tropics, the superheated water around the new volcano must be a welcome interlude.

For a sooty tern the islands are waymarkers in an otherwise featureless ocean.

She could rest here after an endless long flight, yet her feet don't even touch the ground.

Incredibly, once they fledge, sooty terns spend the first four years of their life entirely on the wing.

She may even sleep while flying, waking up if she gets too close to the water.

Her feathers are not waterproofed with oil like other seabirds.

If she gets too wet, she will soak up water like a sponge and drown.

This tern is now a young adult.

Her wandering days are over.

Somewhere in this vast emptiness, she must find a mate and breed.

She heads by instinct for the island of her birth.

Known as Tofua, its smoking crater is a reminder of its violent birth.

Tofua once hosted a thriving tern colony, but there are no other terns to be seen.

Yet there is proof that other birds have tried to nest.

The culprit is not the smoking volcano.

Rats.

Alien invaders, brought here by sailors.

When terns first came to these remote outposts, there were no rats, and so it was relatively safe to nest on the ground.

But seabirds have little defense against the sharp teeth and cunning of rats.

There is nothing for the tern here.

She must move on in search of her own kind.

And she needs to hurry or she will miss the breeding season altogether.

As Tofua is part of the Tongan chain of volcanoes, there are many more islands she can search.

They stand in line, like a petrified army, their heads in the clouds, their feet firmly in the abyss.

The most ancient are as old as the Himalayas, created by similar dramatic collisions of the continental plates.

Sometimes the summit of the volcanic mountain lies just below the surface and corals take advantage of the foothold to form a reef.

Then one day the volcano is pushed up from below and the coral finds itself high and dry.

Corals thrive in sunlight, whereas the world of the strange, blind Alvin shrimp, named after the submersible which first discovered it, lies over a mile below, at the foot of the volcano, in the dark.

Sinking deeper, as the light gradually disappears, the rules by which animals live begin to change.

In the inky blackness, ocean explorers use powerful lights to pick out creatures like jellyfish.

Without these lights, this jellyfish is invisible to us.

But it produces its own light, using a chemical reaction.

The cock-eyed squid can also produce bioluminescent light.

Sometimes it is safer to stay hidden, but it needs light to seduce a partner.

Closer to the bottom, the creatures become more and more alien.

Their bodies are fluid to cope with pressures several hundred times greater than on the surface.

And the water is icy cold.

Because the sun is the source of energy for life on earth, scientists believed that nothing could exist in this dark, cold abyss.

But it turns out to be the richest habitat on our planet, with millions more species than are found up on dry land.

Many newly discovered creatures have yet to be named.

Others are given easily recognizable nicknames, like the Dumbo octopus.

This is the bentnose rabbitfish.

It's probably been around since the time of the dinosaurs.

There are no plants growing on the dark abyssal plains and for a long time biologists believed that all these eccentric creatures survived on tiny food particles falling from the surface.

To some extent this is true.

But most life down here exploits an entirely different source of energy.

The same ring of fire, the same upheavals that created mountains and islands on the surface have sculpted this underwater terrain.

And here too chemical and heat energy explodes into these icy-cold waters from hundreds of mini-volcanoes, known as hydrothermal vents or springs.

White bacteria carpet the flanks of the hot springs like snow and convert the chemical energy into food.

There is so much energy pouring out that the bacteria are overcrowded.

So they sit on any surface they can find, even living squat lobsters.

The lobsters don't mind.

They may even get first pickings.

And in this weird, bleached community, a group of crustacea, known as the Alvin shrimp, has found a niche as a scavenger or cleaner, feeding on everyone else's waste and scraping them clean of bacteria.

There's an entire seafood platter here: squat lobsters, crabs and mussels, all requiring the services of the shrimps.

There are several different species of Alvin shrimp, varying in color from white to yellow or red.

But the bright colors are wasted on the blind shrimp.

Although these shrimps can't see color, they have modified eyes which may be able to detect the infrared heat waves emitted by hot water.

It's a bit like seeing a red-hot iron which glows with heat rather than light.

This allows them to get close enough to the boiling vents to feed, but hopefully not too close, or they will get boiled alive.

The canny Alvin shrimp has found another use for these mini-volcanoes.

The lighter hot water rises rapidly through the icy cold.

These upwellings provide a free ride for any creature needing to travel around the ocean.

So for the adult shrimps stuck at the bottom, the currents provide a springboard for the next generation, which they need to send out into the world.

Alvin shrimps actually hatch as larvae.

They join millions of other eggs and larvae released by the varied community on the seabed, spiraling up through the depths.

But as they grow, it's clear they're very different from their parents.

Unlike them, they have large eyes.

Their eyes are useful, even in the dark, because they can pick out the bioluminescence emitted by carnivores, like the box jellyfish.

Eyes also give them a fighting chance to spot the flashing lights of the Atolla jellyfish.

Yet it is only a chance.

The Alvin larvae have become part of the fast food of the ocean.

But they also need to eat.

The hapless copepod is even more numerous and unfortunately advertises itself with its jerky swimming style.

They're quickly gobbled by jellyfish.

And the acrobatic Alvin larva is partial to copepods too.

The shrimps are slightly better swimmers.

Their feathered feet act as basic oars, which come in useful when facing trouble.

The oars may help against predators as slow as the pudgy cusk eel.

But the glass squid is a far more active and dangerous foe.

It is transparent, which helps camouflage it in the ocean and sneak up on shrimp larvae.

But the squid has one big giveaway.

Its stomach is opaque, so the shrimp can spot it.

For some reason, however the squid moves, its stomach stays upright.

The surviving larvae are swept along as the smaller streams join to form rivers, following the contours of the abyss.

On the riverbed below, giant clams will snap shut on anything which falls within reach.

And in the bottlenecks and canyons, triffid-like carnivores stand in wait.

Gorgonians and crinoids, distant cousins of sea urchins, snatch at or trap the hapless drifters.

When the rivers reach the walls of an underwater volcano, the currents are forced to rise again, taking the Alvin larvae and other plankton with them.

So some shrimps are unwittingly carried into the world of light.

It's not a good place to be.

And as soon as the current releases them, they will try and head back to the dark, cold world below and continue their incredible journey to find a new home in the abyss.

While the Alvin shrimps have produced millions of young, the tern is also busy with the next generation.

Where once she wandered the Pacific, her feet barely ever touching the ground, now she heads straight for this one island known as Hunga Tonga or Mountain of the Tongas.

(birds call) For years she has been a loner.

Now she shares the company of not hundreds, but thousands of birds.

She heads for the heart of the colony.

Sooty terns are known as wide-awake birds for the noise they make.

She dives straight into the fray to find her mate.

Then a quick spruce-up, before she's off again to fish.

With such a quick stopover it looks as though she's hankering after her old life.

But luckily she has the perfect partner to share the nonstop round of babysitting or fishing and he's been left with their egg.

She grabs the chance for a quick break on a floating coconut, while back on the island, the new arrival is minded by the ever-patient male.

She can't stop for long.

The chick needs feeding.

She scans the surface, looking for clues that would indicate some movement below.

The tiny fish she seeks feast on the rising plankton, but unlike many other seabirds, the tern cannot dive deep after them.

She can only circle and watch.

She's waiting for help.

At last, some movement on the water.

A shark fin.

A promising sign.

As the silky sharks circle, the fish panic and pack tighter together as they're pushed up towards the light.

The sea surface acts as a barrier, making them easier to catch.

But they're still too deep for the tern.

A shoal of tuna joins the melee, corralling the fish even tighter, forcing them to leap for their lives.

This is what the terns were waiting for.

Alerted by the hue and cry, more and more hungry terns feast, skimming the surface, barely getting their feet wet.

Relying on tuna is risky and the shoals quickly disappear.

Now she must hurry back with fresh food for her chick.

With tuna becoming scarce, the search has taken her many miles from the island.

But she can read the earth's magnetic field and will navigate by the sun or stars to find the shortest route to her family.

Somewhere in the depths below her, at least one Alvin shrimp larva has survived and is now a young adult.

At its birthplace the original colony is dead.

The underwater volcano hasn't exploded.

It has simply dried up.

Without its chemical energy, there are no bacteria and therefore no life.

A reminder that volcanoes are ephemeral.

They give and they take.

Luckily the young adults are already far away, out in the open ocean.

But like their parents they are now blind.

So they're vulnerable to new dangers.

And every creature they encounter has a different lethal weapon.

The sinuous snipe eel has a world record 750 vertebrae.

Every inch of its sensitive skin is able to detect vibrations.

Providing the shrimp doesn't disturb the water too much, it may just sidle by unnoticed.

More danger ahead.

Getting past the poisonous tentacles of a jellyfish must be like swimming through a minefield.

The shrimp does have one safety mechanism.

It has highly sensitive antennae which can detect vibrations from the slightest movement.

For any shrimp that makes it past the hazards, its antennae could have another crucial role.

Scientists think they can detect vibrations caused by distant, underwater detonations.

They believe this resourceful shrimp doesn't just drift on the current.

It may actively swim to the source of the sounds.

But it is still only tiny.

So when a shrimp meets the walls of another giant underwater mountain, it is once again swept up by the current.

On the slopes, predatory tunicates stand motionless, so even carefully tuned antennae will not detect them.

Out of the thousands of larvae produced by each adult, perhaps a lucky one or two may slip safely past and continue their climb.

The blind shrimp has another useful aid: an acute sense of smell that is able to detect the weakest trace of sulfide in the water.

And finally, like its parents, it can also detect heat.

These finely honed senses, sound, smell and heat, all work in the dark and lead it gradually towards an underwater volcano.

So, by instinct, one tiny Alvin shrimp has navigated the abyss and arrived at one of the most hostile places on earth, bang in the middle of an underwater eruption.

As fire and water fight it out, long before the dust has settled, the Alvin shrimp explores its potential new home.

Life is a little less turbulent on the lower slopes and several other shrimps have already settled in.

Yet the water here is so acidic that the mussels they usually clean can't build their shells.

So for these pioneers trying to start a new colony, there is no seafood platter waiting to be cleaned and the pickings are much leaner.

The crabs are hungry too and squabble among themselves.

The feisty shrimps move in quickly on the dead and injured.

This adaptable diet helps keep them alive in a precarious environment.

But nothing can save them if they stray too close to danger.

Some shrimps are inevitably crushed by falling rocks.

Others are burned by acid or boiled alive.

In this game of Russian roulette, the survivors become cannibals and the biggest shrimps get even fatter.

And, if they're lucky, strong enough to flee the next eruption.

At these freezing-cold temperatures, lava solidifies immediately.

But it's still a precarious pile of bricks on which to build a whole mountain.

One day, sooner or later, the summit will force its way above the surface.

And in what seemed like an empty expanse a new island is born.

Every time a new island forms, the Tongan nation grows.

Often the rock is worn away by wave erosion and disappears.

But this newly emerged island is built from silica which should be hard enough to resist the battering waves.

The sooty tern, passing by after another fishing trip, doesn't understand the significance of the new volcanic activity.

She's simply on her way home to Hunga Tonga to feed her chick.

The island the terns have chosen is a remote paradise, perfect for a breeding colony.

But it is also an active volcano.

And it has suddenly covered most of the island in a deep carpet of ash.

The air should be full of screaming adults and the clamor of chicks.

The wide-awake birds have fallen eerily silent.

In the heart of the tern colony, there's a new crater.

It looks like a luxury heated swimming pool, but its waters are lethal.

The island hasn't settled yet.

Land and water still fight it out.

Pumice stones are witness to the ferocity of the eruption.

And aftershocks rattle the cliffs.

There are signs of violence everywhere.

This is the price terns sometimes pay because they breed on active volcanoes.

But the tern searches for her chick... ..frantically.

(bird calls) (chick cheeps) A few tree-nesters had a lucky escape, but the tern colony was on the ground.

Some of the adults may have flown to safety, but her chick was not old enough to fly.

She's not just looking, she's also trying to listen above the sound of the sea.

(chick cheeps) Each chick's unique signature cry is supposed to help its parents find it in a cacophony of voices in a crowded colony.

(chick cheeps) (adult answers) (cheeps) (cheeps) (adult answers) (cheeps) (adult answers) (cheeps) This cry also comes in useful after a volcanic eruption.

With no sign of the male, it's now entirely down to the female.

She must both protect her chick from further danger and struggle to keep it well fed.

The eruption may be bad news for the terns, but just offshore it's cause for celebration.

Usually these humpback whales continue their long journey to the tropics to find water warm enough to give birth.

But they already have a young calf, which suggests it may have been born here among the volcanic islands.

The humpback family will need to avoid the sulfur clouds.

But these hot springs and recent volcanic activity on other Tongan islands have turned the whole area into a temporary thermal spa.

The timing is perfect for the whales.

They've taken advantage of the eruption, cutting their journey short by thousands of miles, giving them a bit more time to relax.

The female tern is busy fishing again, but with her chick so vulnerable, she can't afford to wander off in search of her allies, the tuna.

She needs to stick close to the island.

Deep in the abyss, the volcano that killed so many terns is a catalyst for new life.

The chemical energy has stimulated the food chain.

And once again plankton hitch a free ride on the hot water currents rising to the surface.

The blue water slicing through the sulfur clouds comes straight from the abyss.

And it is rich with food.

As the sun sets, tiny fish rise in the cover of darkness to feed on the plankton.

And squid race up from the depths to gorge on the fish.

Some of them also dance and court using their natural bioluminescence to dazzle potential partners.

Through her years of wandering the ocean, the tern has learned to read the faintest nighttime signals.

A midnight feast is exactly what she and her fellow survivors need.

(birds call) As soon as dawn breaks, the squid head back down to the depths.

It looks as though she's gobbled the lot and her youngster will go hungry.

The chick knows better.

Its cry actually stimulates the female to regurgitate a cock-eyed squid for breakfast.

And another.

That huge meal, roughly a third of its body weight, will last it little more than 12 hours.

And for its mother, it's straight back to fishing.

She so nearly lost everything to the eruption.

But with so much fast food on offer, it's easier to understand why terns take the risk and nest on these moody volcanic islands.

Not only does the island provide a breeding platform.

The volcano helps send food up from the depths in reach of a seabird who doesn't like to get her feathers wet.

Far below in the abyss, the volcano also brings life and death to the Alvin shrimp.

But this strange blind creature has also adapted to take advantage of the new habitats created by eruptions.

Thanks to the energy from the hydrothermal springs, a new colony of Alvin shrimps is prospering.

Some have already released their larvae to hitch a ride on the rising hot water.

The goal of these young pioneers is to feed and grow, to use their unusual senses to track down the next distant underwater eruption and help spread this unique group of shrimps throughout the dark abyss.

But some will be caught by a current that is too strong and swept up by the walls of the volcano, which helped create them, slowly, unwittingly, towards the hostile world of light.

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